code: def _load_absorption(freqs):
      """Load molar extinction coefficients."""
      # Data from https://omlc.org/spectra/hemoglobin/summary.html
      # The text was copied to a text file. The text before and
      # after the table was deleted. The the following was run in
      # matlab
      # extinct_coef=importdata('extinction_coef.txt')
      # save('extinction_coef.mat', 'extinct_coef')
      #
      # Returns data as [[HbO2(freq1), Hb(freq1)],
      #                  [HbO2(freq2), Hb(freq2)]]
      extinction_fname = op.join(
          op.dirname(__file__),
          "..",
          "..",
          "data",
          "extinction_coef.mat",
      )
      a = loadmat(extinction_fname)["extinct_coef"]
  
      interp_hbo = interp1d(a[:, 0], a[:, 1], kind="linear")
      interp_hb = interp1d(a[:, 0], a[:, 2], kind="linear")
  
      ext_coef = np.array(
          [
              [interp_hbo(freqs[0]), interp_hb(freqs[0])],
              [interp_hbo(freqs[1]), interp_hb(freqs[1])],
          ]
      )
      abs_coef = ext_coef * 0.2303
  
      return abs_coef
  
file_path: mne-python/mne/preprocessing/nirs/_beer_lambert_law.py
imports: import os.path
  import numpy
  from scipy import linalg
  from scipy.interpolate import interp1d
  from scipy.io import loadmat
  from ..._fiff.constants import FIFF
  from ...io import BaseRaw
  from ...utils import _validate_type, warn
  from ..nirs import _validate_nirs_info, source_detector_distances
label_desc: Use image node_id 2 for calling a global function with example usage: _load_absorption(freqs) and returns: abs_coef